Fire tube furnace

ABSTRACT

A fire tube furnace utilizing a plurality of tubular passages through which hot combustion gases pass. A heat exchanging medium is in heat exchanging relationship with the tubular passages, and the passages include inlets having tangentially oriented ports receiving combustion gases directing the gases into the passages in a tangential direction wherein the gases have a spiralling path of movement through the passages. The passages&#39;&#39; outlets are also tangentially oriented to remove combustion gases therefrom with a minimum of back pressure and resistance. Air injection means within the combustion chamber may be used to impart a spiralling gaseous movement within the combustion chamber rotating in a direction aligned with the passages&#39;&#39; inlet port orientation.

[ July 22, 1975 Primary Examinerl(enneth W. Sprague Attorney, Agent, or Firm-Beaman & Beaman [57] ABSTRACT A fire tube furnace utilizing a plurality of tubular passages through which hot combustion gases pass. A heat exchanging medium is in heat exchanging relationship with the tubular passages, and the passages include inlets having tangentially oriented ports receiving combustion gases directing the gases into the passages in a tangential direction wherein the gases have a spiralling path of movement through the passages. The passages outlets are also tangentially oriented to remove combustion gases therefrom with a minimum of back pressure and resistance. Air injection means within the combustion chamber may be used to impart a spiralling gaseous movement within Inventor: Howard R. Johnson, Grass Lake,

Mich.

Assignee: Hush Company, Inc., Wise, Va.

Filed: Apr. 29, 1974 Appl. No.: 465,322

122/156; 122/367 R Int. F22b 7/00 Field of Search 122/41, 155, 156, 115, 122/367 R, 367 A, 367 C References Cited UNITED STATES PATENTS United States Patent Johnson 7 FIRE TUBE FURNACE i m m Eli 17 Claims, 8 Drawing Figures the combustion chamber rotating in a direction aligned with the passages inlet port orientation.

Rees

S ya m n ORB 2507 00 3 9999 1111 2834 1 0940 6408 76 6 95 7 7790 2 SHEET PTENTED JUL 22 ms FIRE TUBE FURNACE BACKGROUND OF THE INVENTION The invention pertains to the field of fire tube furnaces wherein hot combustion gases pass through tubular passages.

Fire tube furnaces are commonly employed as heat exchangers, particularly as boilers for the generation of steam, or the heating of hot water. As the hot combustion gases pass through tubes, or tubular passages, the heat exchanging medium, such as water, surrounding the passages is heated.

The efficiency of a fire tube furnace depends upon several factors, including the efficiency of the heat transfer between the fire tubes and the medium, and the resistance to combustion gas flow within the tubes. Also, the type of material of which the fire tubes are manufactured affects the heat exchange rate between the tubular passages and the heated medium.

It has been known in fire tube furnaces to locate gas flow control means, such as vanes, baffles and the like, within the fire tube to impart a spiralling action to the combustion gases as the gases pass through the tubular passages, as shown in US. Pat. Nos. 1,880,533 and 2,077,776. However, the use of such vanes and baffles increase the resistance to gaseous flow through the passages, and such devices are also subject to rapid deterioration and require periodic replacement.

It has long been appreciated that superior heat exchanging characteristics occur where surface boundary layer effects are minimized within flowing heat exchanging fluids. By imparting a spiralling or swirling motion to a heat exchanging medium passing through a conduit the thermal insulation produced by a boundary layer is reduced, but in the past, guides, vanes and baffles within the passage to produce a swirling or agitation of the heat exchanger fluid significantly increased the resistance to flow, and heavy duty pumps or fans are required in order to maintain high heat exchanging capacities in equipment of relatively concise dimensions.

Further, furnaces of conventional construction of a small size have been limited in heat exchanging capacity, and those small furnaces that have been produced of relatively high heat exchanging capacities are of such complex construction as to require constructions and time consuming manufacturing and assembling techniques, resulting in high cost.

SUMMARY OF THE INVENTION It is an object of the invention to produce a fire tube furnace of concise dimensions wherein hot combustion gases pass through passages or tubes to heat a core in heat exchanging relation to a heat conducting medium. The furnace is provided with means for imparting a swirling motion to the gases as they enter the furnace passages or tubes, and no restrictions are required within the passages to maintain the swirling gaseous action.

Another object of the invention is to provide a fire tube furnace of concise configuration and high efficiency wherein boundary layer effects existing within the fire tubes are reduced, and wherein a swirling buming action is produced within the combustion chamber having a direction of gaseous rotation aligning with inlet ports defined in the fire tube passages to contribute to the swirling action achieved within the passages.

In the practice of the invention a core formed of a metal having high thermal conductivity characteristics is provided with a plurality of elongated passages through which the hot gases of combustion pass. A combustion chamber located at one end of the core is in communication with an inlet end of the fire tube passages, and a flue communicates with the other end of the passages. The passages inlet ends are each provided with a tangentially related port in the form of an elongated slot whereby the combustion gases entering the passages from the combustion chamber tangentially enter the passages and are thereby imparted a swirling action which continues as the gases pass through the fire tube passages.

The exhaust end of the passages is also provided with a tangentially oriented port whereby the combustion gases are ejected from the passages with a minimum of resistance and back pressure, and enter the flue.

The swirling action of the combustion gases as they enter the fire tube passages is preferably augmented by a swirling turbulance existing in the combustion chamber having a direction of movement aligned with the tangential orientation of the inlet ports. This swirling action within the combustion chamber results from the oblique orientation of air passages providing air to the combustion chamber.

Transfer of heat from the combustion chamber to the core is also augmented by the existance of heat sinks in direct alignment with the combustion burner nozzle, and as the heat sink is directly affixed to the core transfer of heat from the heat sink to the passages readily occurs.

In a variation of the basic concept the core includes a central passage having means for spirally directing the heat exchanging medium as it moves therethrough. Further, the invention contemplates the use of a plurality of fire tube passages defined in the core for receiving the combustion gases wherein the passages are interconnected in pairs such that combustion gases flowing through a single inlet port or slot pass through the core through a pair of parallel passages, and the passages of an associated pair include tangentially interconnected openings whereby the spiralling action of the combustion gases exist in all fire tube passages, and the gases are ejected from the passages in a tangential manner with a minimum of back pressure and resistance.

BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned objects and advantages of the invention will be appreciated from the following description and accompaning drawings wherein:

FIG. 1 is a diametrical, elevational, cross-sectional view of a fire tube furnace in accord with the invention,

FIG. 2 is a plan, sectional view as taken along section II-Il of FIG. 1,

FIG. 3 is a plan, sectional view as taken through section IIIIII of FIG. 1,

FIG. 4 is a plan, sectional view taken through the passages inlet ports along section IV-IV of FIG. 1,

FIG. 5 is a view similar to FIG. 1 illustrating a variation of embodiment utilizing a heat exchanging medium guide within the core passage,

FIG. 6 is a plan, sectional view taken through the exhaust ports of the passages along section VI-VI of FIG. 5,

FIG. 7 is a plan, sectional view taken along section VIIVII of FIG. 5, and

FIG. 8 is a plan, sectional view taken along section VIIIVIII of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT The relationships of the components of the fire tube furnace in accord with the invention will be appreciated from FIG. 1. The furnace includes an elongated core 10 of generally cylindrical configuration formed of a metal having high heat transfer characteristics, such as aluminum or copper.

The core 10, includes a lower end 12, and an upper end 14, an outer cylindrical surface 16, a central elongated cylindrical passage 18, a plurality of fire tube passages 19 deposed parallel to each other and the central passage, an inlet passage 20 communicating with the core upper end 14 and the passage 18, and an outlet heat exchanging medium passage 22 communicating with the central passage 18 and the outer surface 16.

The lower end of the core 10 is provided with a plurality of ports or slots 24, FIG. 4, which communicate with the chamber 26 formed by the lower end of the passage 18, and the passages 19. As appreciated from FIG. 4, each port 24 is tangentially located to its associated fire tube passage 19, and is also substantially tangentially disposed to the chamber 26.

At the upper end 14 of the core the fire tube passages 19 are also provided with tangentially disposed outlet exhaust ports or slots 28, FIG. 2, and these ports communicate with an exhaust chamber 30 defined at the upper end of the central passage 18.

The central passage 18 is sealed near its upper end by a sealing plate 32 welded to the core, and the lower end of the passage is sealed by a heat sink 34 consisting of a pair of copper plates brazed to the core 10.

The core 10 is encased within a cylindrical casing 36 having an internal diameter greater than the diameter of the core whereby an annular passage 38 exists between the core and casing. The lower end of the casing is sealed by a combustion chamber defining head 40 brazed or welded to the core and casing having a central recess defining the combustion chamber 42. The head 40 includes a burner nozzle 44 mounted therein to which the fuel, such as natural gas, is supplied to the combustion chamber. Ignition of the fuel is preferably accomplished by an electric ignitor 46 of conventional construction. Air is supplied to the combustion chamber 42 through a plurality of air passages 48 formed in the head, one of which is shown in FIG. 1. The air passages 48 are preferably obliquely related to the axis of the combustion chamber, and burner nozzle, such that the air introduced therethrough into the combustion chamber causes a swirling action of the burning gases within the combustion chamber in a direction aligned with the fire tube inlet ports 24, as indicated by the arrows in FIG. 4. A motorized fan or air pump 50 may be connected to the passages 48 for forcing air into the combustion chamber 42.

The upper end of the casing 10 is enclosed by a head 52 welded or brazed to the casing and core. The head 52 includes a central opening 54 communicating with the core exhaust chamber 30, and a flue 56 is affixed to the head in alignment with the opening 54. An inlet fitting 58 for the heat exchanging medium is mounted in the head 52 in alignment with the core passage 20.

The head 40 is sealed to the lower end 12 of the core 10, and in a similar manner the head 52 is sealed to the core upper end 14.

An outlet fitting 60 for the heat exchanging medium is defined in the casing 36, FIG. 1, adjacent the head 52 wherein a heat exchanging medium, such as water, or a mixture of water and an anti-freezing liquid, may be introduced into the central core passage 18 through the passage 20 and the fitting 58, and passes to the exterior of the core through the passage 22, and about the core through annular passage 38 to the outlet fitting 60 for distribution to radiators and similar heat exchanging apparatus.

The hot combustion gases within the combustion chamber 42 and the core chamber 26 pass upwardly through the fire tube passages 19 in a spiralling manner throughout the length of the passages. This spiralling action of the combustion gases results from the tangential introduction of the gases into the passages through the inlet ports 24. Thus, as the gases pass upwardly through the cylindrical fire tube passages 19 the spiralling action initially imparted to the gases eliminates boundary layers which might otherwise exist at the fire tube or passage surfaces and reduce the efficiency of heat transfer between the gases within the passages and the core 10.

Upon the combustion gases reaching the exhaust ports 28 the heat transfer between the gases and the core will be substantially completed, and the gases are removed from the passages through ports 28 in a tangential direction aligned with the direction of combustion gas movement as will be appreciated from the arrows in FIG. 2. The tangential orientation of the exhaust ports 28 insures the absence of back pressure at the exhaust ports, and thus no resistance to the spiralling action within the fire tube passages results throughout the length of the passages.

Heat transfer from the heat sink 34 to the core 10 is also efficiently accomplished due to the bonding of the heat sink to the core, and the alignment of the heat sink with the burner nozzle. Further, as the annular passage 38 extends about the head 40 radiated heat from the burner to the head will be transferred to the heat exchanging medium surrounding the head.

Fire tube furnaces constructed in accord with the invention have high efficiency of heat transfer in small sizes. For instance, a furnace in accord with the invention approximately one foot in length and seven inches in diameter is capable of producing in excess of 100,000 BTU output. Such furnaces may be efficiently utilized with hot water heating systems, and readily lend themselves for use with combination heating and cooling systems exteriorly located from the space being serviced. It has been discovered that the furnace of the invention produces unusually low polluting emissions, which is attributed to the relationship of furnace components and the rapid transfer of heat to the core.

FIGS. 5 through 8 illustrate a variation in the construction of a fire tube furnace utilizing the inventive concepts. As many of the components of this embodiment are identical to those previously described, such components are indicated by primed referenced numerals, and will not be further described or explained.

In the embodiment of FIGS. 5 through 8 the central core passage 18' is provided with a spiralled baffle 62 wherein the heat exchanging medium introduced into the passage 18' through the passage 20 moves in a spiral manner through the passage 18' thereby assuring a turbulence and spirallingaction of the heat exchange medium within the central passage which improves heat transfer from the core tothe medium. While the existence of the baffle 62 does add a resistance to heat exchanging medium flow through the furnace, the fact that the medium is necessarily pumped through the furnace prevents such resistance from becoming a serious detraction of the efficient character of the furnace.

In FIG. 5 a slight variation in the configuration of the heat sink 64 is illustrated as the heat sink is provided with a concave surface 66, and an enlarged area of contact exists between the heat sink and the core 10'. The heat sink is welded or bonded to the co re such that an efficient heat transfer between the heat sink and core takes place. i

In the embodiment of FIGS. 5 through 8 the fire tube passages are formed in pairs wherein each passage 19 has a similar passage 70 associated therewith. Associated pairs of passages are interconnected at the inlet end, FIG. 8, by interconnecting ports 72 tangentially related to both passages. Thus, combustion gases entering the ports 24, and the passages 19', enter the associated passages 70 through the interconnecting ports 72, and a spiralling action occurs within the combustion gases passing through both passages 19 and 70.

In like manner the exhaust end of the fire tube passages 19' and 70 are provided with interconnecting ports 74 tangentially related to the passages whereby the combustion gases may pass from a passage 70, into a passage 19' and directly into the chamber through the exhaust ports 28.

The aforementioned use of pairs of passages 19 and 70 increases the area of contact between the combustion gases and the core 10', and permits an even greater reduction in the size of the furnace as compared with the embodiment of FIG. 1 for a given furnace capacity.

It will be appreciated from the above that the objects of the invention are achieved by the disclosed embodiments and it is understood that modifications within the inventive concept of the invention may be apparent to those skilled in the art.

What is claimed is:

1. A fire tube furnace comprising, in combination, an elongated core of heat conductive material, a heat transfer surface defined on said core for engagement with a medium to be heated, a plurality of elongated passages defined in said core each having an inlet and an outlet axially spaced with respect to each other, a combustion chamber communicating with said passages inlet, burner means within said combustion chamber, flue means communicating with said passages outlet, and combustion gas flow control means located at said passages inlets tangentially introducing combustion gases into said passages whereby gases introduced into and passing through said passages have a spiralling path of movement.

2. In a fire tube furnace as in claim 1 wherein said gas flow control means comprises a port defined in said core tangentially related to the associated passage and communicating with said combustion chamber.

3. In a fire tube furnace as in claim 2 wherein said ports comprise slots having a length substantially parallel to the length of the associated passage.

4. In a fire tube furnace as in claim 1, a heat exchanging medium passage defined in said core, the surface of said passage defining at least a portion of said heat transfer surface, and medium inlet and outlet means communicating with said passage.

5. In a fire tube furnace as in claim 1, a casing encompassing said co're, said core having an outer surface radially spacedfrom said casing whereby an annular chamber is defined between said core outer surface and casing, said outer surface constituting a heat transfer surface, and heat exchanging medium inlet and outlet rnearis communicating with said chamber.

' 6. In a fire tube furnace as in claim 2, wherein said passages each include an outlet port communicating with said flue means, said outlet ports being defined in said core and tangentially intersecting the associated passage in a direction aligned with the spiralling path of movement of medium within the associated passage.

7. In a fire tube furnace as in claim 6, second passages defined in said core adjacent said passages and parallel thereto, interconnecting ports interconnecting each second passage with a passage adjacent said combustion chamber and said flue means, said interconnecting ports being tangentially related to the associated passage'and second passage.

8. In a fire tube furnace as in claim 1 wherein said core includes a central elongated passage defined therein, the surface of said passage comprising a heat transfer surface and heat exchanging medium inlet and outlet means communicating with said central passage.

9. In a fire tube furnace as in claim 8, a spiral baffle within said central passage producing a spiralling flow path for heat exchanging medium flowing therethrough.

10. In a fire tube furnace as in claim 1, air injection means communicating with said combustion chamber injecting air into said combustion chamber to swirl the gases within said chamber in a direction aligned with said gas flow means.

11. A fire tube furnace for heating a fluid heat exchanging medium comprising, in combination, an elongated core having first and second ends and an outer surface, a plurality of elongated cylindrical passages defined in said core extending in the direction of the core length each having an inlet and an outlet axially spaced with respect to each other, a casing surrounding said core having an inner surface spaced form said core outer surface defining an annular chamber therebetween, a combustion chamber located adjacent said core first end and communicating with said passages inlet, burner means within said combustion chamber, a flue communicating with said passages outlet adjacent said core second end, a flow passage centrally defined in said core extending in the direction of the length of said core, a connecting passage defined in said core establishing communication between said central passage and said annular chamber, medium inlet and outlet fittings communicating with said central passage and said annular chamber, and inlet ports defined at said passages inlet tangentially disposed to the associated passage tangentially introducing combustion gases into said passages producing a spiralling path of movement of combustion gases through said passages.

12. In a fire tube furnace as in claim 11, outlet ports defined in said core at said passages outlets communicating with said flue and tangentially related with the associated passage in a direction aligned with the spiralling path of medium movement within said passages.

13. In a fire tube furnace as in claim 12 wherein said inlet and outlet ports comprise slots having a length substantially parallel to the length of the associated passage.

14. In a fire tube furnace as in claim 13, air injection means communicating with said combustion chamber injecting air into said combustion chamber to swirl the gases within said chamber in a direction aligned with said gas flow means.

15. A fire tube furnace comprising, in combination, a supporting member, a plurality of substantially parallel tubular passages defined on said support member and each having an inlet end and an outlet end, a combustion chamber communicating with said tubular passages inlet ends, flue means communicating with said tubular passages outlet ends, means circulating a heat exchanging medium in heat exchanging relationship to said tubular passages, and combustion gas flow control means located at said tubular passages inlet endstangentiallyintroducing combustion gases into said tubular passages whereby gases introduced into and passing through said tubular passages have a spiralling path of gas flow control means comprise slots having a length parallel to the length of the associated tubular passage. 

1. A fire tube furnace comprising, in combination, an elongated core of heat conductive material, a heat transfer surface defined on said core for engagement with a medium to be heated, a plurality of elongated passages defined in said core each having an inlet and an outlet axially spaced with respect to each other, a combustion chamber communicating with said passages'' inlet, burner means within said combustion chamber, flue means communicating with said passages'' outlet, and combustion gas flow control means located at said passages'' inlets tangentially introducing combustion gases into said passages whereby gases introduced into and passing through said passages have a spiralling path of movement.
 2. In a fire tube furnace as in claim 1 wherein said gas flow control means comprises a port defined in said core tangentially related to the associated passage and communicating with said combustion chamber.
 3. In a fire tube furnace as in claim 2 wherein said ports comprise slots having a length substantially parallel to the length of the associated passage.
 4. In a fire tube furnace as in claim 1, a heat exchanging medium passage defined in said core, the surface of said passage defining at least a portion of said heat transfer surface, and medium inlet and outlet means communicating with said passage.
 5. In a fire tube furnace as in claim 1, a casing encompassing said core, said core having an outer surface radially spaced from said casing whereby an annular chamber is defined between said core outer surface and casing, said outer surface constituting a heat transfer surface, and heat exchanging medium inlet and outlet means communicating with said chamber.
 6. In a fire tube furnace as in claim 2, wherein said passages each include an outlet port communicating with said flue means, said outlet ports being defined in said core and tangentially intersecting the associated passage in a direction aligned with the spiralling path of movement of medium within the associated passage.
 7. In a fire tube furnace as in claim 6, second passages defined in said core adjacent said passages and parallel thereto, interconnecting ports interconnecting each second passage with a passage adjacent said combustion chamber and said flue means, said interconnecting ports being tangentially related to the associated passage and second passage.
 8. In a fire tube furnace as in claim 1 wherein said core includes a central elongated passage defined therein, the surface of said passage comprising a heat transfer surface and heat exchanging medium inlet and outlet means communicating with said central passage.
 9. In a fire tube furnace as in claim 8, a spiral baffle within said central passage producing a spiralling flow path for heat exchanging medium flowing therethrough.
 10. In a fire tube furnace as in claim 1, air injection means communicating with said combustion chamber injecting air into said combustion chamber to swirl the gases within said chamber in a direction aligned with said gas flow means.
 11. A fire tube furnace for heating a fluid heat exchanging medium comprising, in combination, an elongated core havinG first and second ends and an outer surface, a plurality of elongated cylindrical passages defined in said core extending in the direction of the core length each having an inlet and an outlet axially spaced with respect to each other, a casing surrounding said core having an inner surface spaced form said core outer surface defining an annular chamber therebetween, a combustion chamber located adjacent said core first end and communicating with said passages'' inlet, burner means within said combustion chamber, a flue communicating with said passages'' outlet adjacent said core second end, a flow passage centrally defined in said core extending in the direction of the length of said core, a connecting passage defined in said core establishing communication between said central passage and said annular chamber, medium inlet and outlet fittings communicating with said central passage and said annular chamber, and inlet ports defined at said passages'' inlet tangentially disposed to the associated passage tangentially introducing combustion gases into said passages producing a spiralling path of movement of combustion gases through said passages.
 12. In a fire tube furnace as in claim 11, outlet ports defined in said core at said passages'' outlets communicating with said flue and tangentially related with the associated passage in a direction aligned with the spiralling path of medium movement within said passages.
 13. In a fire tube furnace as in claim 12 wherein said inlet and outlet ports comprise slots having a length substantially parallel to the length of the associated passage.
 14. In a fire tube furnace as in claim 13, air injection means communicating with said combustion chamber injecting air into said combustion chamber to swirl the gases within said chamber in a direction aligned with said gas flow means.
 15. A fire tube furnace comprising, in combination, a supporting member, a plurality of substantially parallel tubular passages defined on said support member and each having an inlet end and an outlet end, a combustion chamber communicating with said tubular passages inlet ends, flue means communicating with said tubular passages outlet ends, means circulating a heat exchanging medium in heat exchanging relationship to said tubular passages, and combustion gas flow control means located at said tubular passages'' inlet ends tangentially introducing combustion gases into said tubular passages whereby gases introduced into and passing through said tubular passages have a spiralling path of movement.
 16. In a fire tube furnace as in claim 15, outlet gas flow control means located at said tubular passages'' outlet ends communicating with said flue means and tangentially related to the associated passage in a direction aligned with the spiralling path of medium movement within said passages.
 17. In a fire tube furnace as in claim 16 wherein said gas flow control means comprise slots having a length parallel to the length of the associated tubular passage. 